Nontamperable fuse



April 26, 1938. J. A. MCENTEE 2,115,447

NONTAMPERABLE FUSE v 42 f2 figg,

W f wf- W Patented Apr. 26, 1938 UNITED STATES PATENT OFFICE NONTAMPEBABLE FUSE Application March 5,

19 Claim.

This invention relates to electric fuses and particularly to non-tamperable plug fuses.

This invention in some respects is intended as an improvement on the invention disclosed in the copending application of Elmer H. Taylor, Serial No. 41,559, filed September 21, 1935, which is assigned to the assignee of the present application.

A non-tamperable plug fuse is one that is so arranged that the terminals of the socket or receptacle that receives it cannot be bridged readily by improper materials held in the receptacle by the blown receptacle plugin an attempt to restore electric service mterrupted by the blowing of the plug.

The non-tamperable fuse usually comprises a plug that carries the fusible element and an adapter intended to be 'more or less permanently retained in the plug receptacle, the plug and adapter having cooperating elements that provide the desirable feature of non-tamperability.

It has been found desirable to have these cooperating elements interflt or mesh so closely that a bridging member of the order of tin-foil or a thin wire cannot readily be lodged between them. It is also desirable to form the plug body which encloses the fusible element of some inorganic material, or one which is inert and does not liberate gas when subjected to the arc formed upon rupture of the fusible element upon heavy overload. A body material such as porcelain, however, cannot be molded economically tm the close dimensions required for the intertltting of the non-tamperable elements. An organic body such as an articial resin and particularly a resinous phenol condensation product can be molded within the desired close limits but is not entirely satisfactory as an enclosure for the fusible element because it liberates gas when subject to the heat of a heavy circuit interrupting arc.

Hence an object of the present invention is the provision of a non-tamperable plug fuse wherein the plug body enclosing the fusible element or link comprises an inert material as porcelain and wherein the non-tamperable elements comprise Aa separate body formed of some material, as an artificial resin, that is not necessarily inert when subjected to an electric arc but which can be molded to accurate dimensions, and means such as the screw-threaded terminal shell of the fuse to hold the two bodies together to form in effect an integral structure.

A further object of the invention is the provision of a non-tamperable plug fuse comprising a plug body of inert material as porcelain hav- 1936, Serial N0. 87,266

(Cl. 20G-119) ing an internal fusible element containing chamber closed at the bottom by a bottom wall integral with the plug body and closed at the top by a separate cap member, the fuse having a separate member carrying the non-tamperable elements, said member being held against the integral wall of the chambered body by suitable means as the screw-threaded terminal shell of the fuse.

It is desirable to provide a non-tamperable construction such that the plug can be received in a standard fuse receptacle that does not have a non-tamperable member, or adapter, therein; and such a construction constitutes another object of the invention.

A yet further object is the provision of a plug `fuse and also an adapter therefor having a circuit controlling contact member of such small axial dimensions that the center contact member of the plug can engage it and also can engage the center contact of the receptacle when the adapter is not in the receptacle, thereby to adapt the plug for use in receptacles not having an adapter.

Another object is generally to improve the construction of fuses.

Fig. 1 is a sectional elevation through a fuse embodying the present invention in the circuit conducting relation of the parts.

Fig. 2 is a fragmentary section similar to Fig. 1 but showing the plug partly out of operative position and the movable contact member of the adapter in open circuit position.

Fig. 3 is a perspective view of the fuse plug body of Fig. 1.

Fig. 4 is a perspective view of the non-tamperable member of the fuse plug of Fig. 1.

Fig. 5 is a perspective view of the adapter of Fig. 1.

Fig. 6 is a plan view of the movable contact member of the adapter.

Fig. 7 is a sectional detail illustrating a modied manner of accurately-registering the plug body and tamper-preventing section co-axially.

The fuse embodying the present invention is adapted to be located in a socket or receptacle comprising an insulating base I0 having, usually, a circular upstanding insulating flange I2 within the well of which an internally screw-threaded shell I4 is located, which shell is connected to a conductor terminal It of the base by a conducting strap il. The receptacle has a center contact member Il located in the bottom of the well and co-axially therewith and is connected by a strap 22 with a second conductor terminal 24 of the base.

The receptacle as thus constructed is arranged to receive a so-called standard plug fuse having an outer screw-threaded shell adapted to be screwthreaded in the terminal shell I4 and a center contact member adapted to engage the center contact member 28. With such a plug the contact terminals of the receptacle can be bridged readily by inserting metal foil, wire and the like within the receptacle and holding the bridging material in place under a blown standard plug.

For the purpose of rendering it diiicult to bridge the terminals of, or tamper with, the fuse and the receptacle, an adapter 26 is inserted in the receptacle, in the bottom of the shell I4 and over and, for many receptacles, upon the center contact member 20. The body of said adapter is composed of insulating material, preferably a molded artificial resin, that can be molded accurately to dimensions. The adapter is formed with a lower cylindrical body or flange 28 which is externally screw-threaded and is screwthreaded in the internal threads of the receptacle shell I4. Means such as one or more projecting resilient locking members 36 are, or can be, carrled by the adapter to dig into the receptacle shell when it is attempted to screw the adapter out of the shell, for the purpose of irremovably locking the adapter in place.

The adapter also is formed with an upstanding cylindrical boss or projection 32 which is co-axial with the threaded flange 28. Said boss is surrounded by a circular rib 34 which is co-axial with the boss and preferably is level therewith and is circularly spaced therefrom to provide an annular recess 36 which preferably is deeper than the height of said rib. 'I'he top of said rib is formed or provided with a series of angularly spaced sharp-edged notches 38 in which bridging material such as a fuse wire is adapted to be caught and sheared off by the rotation of the cooperating plug presently to be described.

The adapter is provided with a movable contact member 48 adapted to be engaged by the center contact member of the plug and moved thereby into engagement with the center contact member 20 of the receptacle but is normally biased for, movement out of engagement with said receptacle contact member. Said contact member 40 is of small axial length so that the plug which cooperates with the adapter can also be inserted in and make operative engagement with the center contact member of a similar receptacle not having the adapter.

Said contact member 48 comprises a cup-shaped member having a thin bottom wall 44 which is adapted to engage the receptacle contact member 28. The cup shaped member is carried by or, as here shown, ls integral with resilient means which act to urge the cup-shaped member upwardly. Said resilient means comprise a plurality -of outwardly extended resilient arms 46. Said contact member 48 is located in a circular recess 48 formed in the lower face of the adapter. The bottom end of said recess is closed by an insulating plate 58 which is pressed into an enlargement of said recess. Said cover plate is provided with a circular passage 52 therethrough which is coaxial with the adapter. The cup member 42 of the contact member is movable axially in said passage into and out of engagement with the center contact member of the receptacle. The spring arms 46 are reilexed downwardly and the ends thereof constantly bear against the inner face of said cover plate and tend to urge the upper part of the contact member against the bottom wall of the recess 48, which is the normal open circuit position of the contact member. In this position the cup shaped member preferably is within the upper end of the passage-l52- 'I'he boss 32 is provided with a small diameter axial passage 53 adapted to permit access of the center contact member of the associated plug to said contact member 48.

YThe plug associated with the adapter comprises a cylindrical body 54 composed of a molded inorganic material that is inert or does not give oil.' gas and is not otherwise harmfully affected by the heat of the circuit interrupting arc. At present porcelain is the best material known to me.

Said cylindrical body is provided with a fuse link chamber or recess 56 which is closed at the bottom by a flat porcelain wall 58 that is integral with the cylindrical side wall. The chamber is open at its upper end and is closed by a transparent window preferably by mica 60 which is heldin place on the end of the cylindrical body by a centrally apertured metal cap 62 having a side wall the end 64 of which is reflexed about the lower edge of the outstanding notched flange 66 of the plug body.

' The plug body is provided with external screw threads 68 on which is located an interiorly and exteriorly screw-threaded metalshell 10 which constitutes a terminal of the plug body. Said shell is adapted to be screwed into and electrically engage the vshell I4 of the receptacle.

The plug body is provided with a center contact member 12 in the form of a relatively long, small diameter cylindrical metal rod located coaxially with the plug body and secured in the bottom wall 58 and projecting downwardly therefrom and also into the link chamber 56. A fusible element or fuse link 14 has one end connected with the upper end of the contact member 12. The other end of the link is located in a channel 16 of the plug body and is connected to the terminal shell 10 by a mass of solder 18. Said solder mass also serves as a key to hold the terminal shell against rotation on the plug body.

'Ihe plug is provided with non-tamperable means cooperating with the boss 32, rib 34 and channel 36 of the adapter, said means, however, being a part of a member 88 that is separate from the plug body. Said member 88 comprises a flat upper circular wall 82 from the periphery of which depends an outer annular rib 84 and, internally spaced therefrom, an inner annular rib 86.

providing an annular channel 88 between the ribs and a cylindrical passage 88 within the inner rib. The inner rib 86 is adapted to fit snugly into the annular recess 36 of the adapter and the outer rib 34 of the adapter is adapted to fit snugly in the annular recess 88 of said member 80. The outer rib 84 surrounds the adapter rib 34 and the inner rib 86 surrounds the adapter boss 32. The inner rib 86 preferably depends substantially below the outer rib 84. The bottom face of the inner rib is provided with a series of angularly spaced sharp-edged notches 92 which cooperate with the notches 38 of the adapter in catching and shearing oif bridging material.

, The radial clearance between the intermeshing ribs is intended to be as small as practical so that bridging material cannot occupy the space between the confronting faces of the intermeshed ribs. For this purpose the member is molded in the above described shape and is composed of some moldable material as an artificial resin that can be molded accurately to dimension.

The terminal shellllof the plug body surrounds and engages the periphery 'of said member Il and has its inwardly extended lower end flange 94 seated upon the bottom face of the rib Il, whereby to hold the flat wall l2 of said member 80 seated upon the bottom face of the wall 5l of the plug body.

The terminal shell 1I serves to locate the member 80 co-axial with the center'contact. member 12. The wall 82 of said member is provided with a pair of upstanding projections 90 which are snugly received in correspondingly shaped recesses 9B in the end wall 5I additionally to locate the member 80 co-axially with the plug body and also to keep the two together for conjoint rotation.

With the above arrangement the accurate dimensioning property of the member 8l can be utilized and yet the member is entirely excluded from the arc formed upon the fusing of the fusible element or link 'Il under excessive current, while the arc takes place in an enclosure the walls of which do not liberate gas into the fuse chamber when subject to the arc.

The small axifl length of the adapter contact member 4|) and the long center contact member "I2 of the plug, which contact member projects beyond any insulating part of the plug, adapts the plug for service both in a fuse receptacle having an adapter therein and also in a receptacle having no adapter therein.

In the modification illustrated in Rg. 7 a different manner of locating the tamper-preventing member 80 co-axially with the center contact member 12 of the fuse is shown. In this modification the central passage 90 is provided with a transverse top wall Illl that has a central passage |02 therein in which the center contact member 12'is adapted to fit snugly. The passage |02 can be accurately located co-axially with the ribs B4 and 86 and thus the ribs can be accurately located co-axially with the center contact member and hence with the ribs of the adapter.

I claim:

l. A non-tamperable plug fuse comprising the combination of a plug body having means providing a chamber, a fusible member in said chamber, a member on the end of said body having tampa-preventing means exposed at the bottom end of the member, means irremovably securing said body and member together, and fuse terminals connected with said fusible member.

2. A non-tamperable plug fuse comprising a body having a fuse link chamber therein, a bottom wall for said chamber integral with said body, a separate closure for the top of said chamber, a member on the bottom face of said wall having tamper-preventing means, means irremovably securing said body and member together, a fusible link in said chamber, and terminals connected with said link.

3. A non-tamperable plug fuse comprising a porcelain body having a fuse link chamber therein and a bottom wall for said chamber that is integral with said body, a closure for the open top of said chamber, a member` on the bottom face of said wall having tamper-preventing means and composed of a molded artificial resin,

means irremovably securing s aid body and member together, and a fusible link in said chamber.

4. A non-tamperable plug fuse having a chambered ceramic body, a fusible link in the chamber, a member on the end of said body composed of an articial resin having tamper-preventing means exposed at the end of the plug, fuse ter minals, means irremovably securing said body and member together, and means isolating said member from the action of the arc formed by the rupture of said link.

5. A non-tamperable plug fuse comprising an externally screw-threaded plug body having a fuse link chamber therein and a bottom wall integral with said body and closing said chamber at the bottom, a closure for the top of said chamber, a center contact member .carried by said bottom wall and projecting downwardly therebelow, a screw-threaded terminal shell on the screw-threads of said body, a fusible link within said chamber and connected between said contact member and shell, a member separate from said body on said bottom wall and having an annular tamper-preventing recess in its ,end face, said screw shell having means clamping said member on said bottom wall, and means securing said member and plug body irremovably in the aforesaid relation. n

6. A non-tamperable plug fuse comprising a screw-threaded plug body having a fuse link chamber therein and a bottom wall integral with said body and closing said chamber at the bottom, a closure for the top of said chamber, a center contact member carried by said bottom wall and projecting downwardly therebelow, a screw-threaded terminal shell on the screw threads of said body, a fusible link within said chamber and connected between said contact member and shell, a member separate from said body on said bottom wall and having an annular tamper-preventing recess in its end face, said screw shell having means clamping said member on said bottom wall, and means securing said member and plug body in the aforesaid relation, said center contact member projecting through and beyond said member.

7. A non-tamperable plug fuse comprising a screw-threaded plug body having a fuse link chamber therein and a bottom wall integral with said body and closing said chamber at the bottom, a closure for the top of said chamber, a center contact member carried by said bottom wall and projecting downwardly therebelow, a screw-threaded terminal shell on the screw threads of said body, a fusible link within said chamber and connected between said lcontact member and shell, a member separate from said body on said bottom wall and having an annular tamper-preventing recess in its end face, said screw shell having means clamping said member on said bottom wall, means securing said member and plug body in the aforesaid relation, said member composed of an arc-reactive material capable of being molded to accurate dimensions, and said plug.body composed of an arc inert moldable material.

8. A plug fuse comprising a body having a chamber therein and a bottom wall integral with said body forming a bottom closure for said chamber, a closure for the top of said chamber, an insulating tamper-preventing member separate from said body and disposed on the end thereof and on said bottom wall, means permanently securing said body and member in the aforesaid relation, terminals carried by said body, and a fusible member in said chamber connected with said terminals.

9. A `non-tamperable plug fuse comprising a plug body having a fuse link chamber therein and a bottom wall integral with said body and closing said chamber at the bottom, a closure for the top of said chamber, a center contact member carried by said bottom wall and projecting downwardly therebelow, a screw-threaded terminal shell on said body, a fusible link within said chamber and connected between said contact member and shell, a member separate from said body on said bottom wall and having outer and inner radially spaced' annular tamper-preventing ribs projecting endwise of said plug, said inner ribs surrounding and spaced from said center contact member, means positioning said ribs and contact member co-axially, and means irremovably securing said member to said plug body.

10. A non-tamperable plug fuse comprising a plug body having a fuse link chamber therein and a bottom wall integral with said body and closing said chamber at the bottom, a closure for the top of said chamber, a center contact member carried by said bottom wall andprojecting downwardly therebelow, a screw-threaded terminal shell on said body, a fusible link within said chamber and connected between said contact member and shell, a member separate from said body on said bottom wall and having outer and inner radially spaced annular tamper-preventing ribs projecting endwise of said plug, said inner ribs surrounding and spaced from said center contact member, means positioning said ribs and contact member co-axially including interiitting projections and indentations of said member and end wall, and means securing said member irremovably on said plug body.

11. A non-tamperable plug fuse comprising a plug body having a fuse link chamber therein and a bottom wall integral withsaid body and closing said chamber at the bottom, a closure for the top of said chamber, a center -contact member carried by said bottom wall and projecting downwardly therebelow, a screw-threaded terminal shell on said body, a fusible link within said chamber and connected between said contact member and shell, a member separate from said body on said bottom wall and having outer and inner radially spaced annular tamper-preventing ribs projecting endwise of said plug, said inner ribs surrounding and spaced from said center ccntact member, means positioning said ribs and contact member co-axially, said member being located within said shell, and said shell having an inwardly directed end flange seated upon the end face of said outer rib which clamps said member upon said plug body, and means permanently anchoring said shell to said plug body.

12. The combination of a plug fuse and an adapter having cooperating conductor dislodging and rupturing means, said fuse having a terminal shell and' a center contact member that projects a substantial distance beyond the end of the fuse, and said adapter comprising an insulating body adapted to be located in a fuse receptacle over the center contact thereof and a movable contact member resiliently supported by said body and adapted to be engaged by the fuse contact member and moved thereby into engagement with the receptacle center contact, said w movable contact member being of such short chamber therein, a bottom wall integral with said body and constituting a closure for the bottom of said chamber. a closure for the top of said chamber separate from said body, a terminal shell on said body, a center contact member carried by and extended below said bottom wall, a fusible element in said chamber and connected with said shell and contact member, and a tamper-preventing member separate from said body on said bottom wall having outer and inner spaced projecting annular ribs surrounding said contact member, means irremovably securing said member and plug body together, said adapter comprising a member having means providing screw threads, an outer upstanding annular rib adapted to enter the space between the ribs of said fuse, a center upstanding boss having a fuse contact passage therein and adapted to enter the space within the inner rib of said fuse, and a movable contact member under the passage of said boss.

14. The combination of a fuse receptacle having a terminal shell and a center contact member, a fuse having a center contact member and a terminal shell engaged with said receptacle shell, an adapter comprising an insulating body within said shell over said receptacle contact member and under said fuse, a movable contact member carried by said insulating body adapted to be clamped between the center contact members of said fuse and receptacle, and means acting on said body and contact member constantly ,biasing said movable contact member for movement away from said receptacle contact member, said movable contact member being thin in the axial direction of the receptacle to permit direct engagement of the fuse contact member with the receptacle contact member when the adapter is absent from the receptacle, said fuse and adapter also having cooperating conductor dislodging and rupturing means.

15. An adapter for fuses and fuse receptacles comprising an insulating member having a passage therethrough, a movable contact member carried by said insulating member and located in a part of said passage and including a thin contact plate that traverses said passage and has oppositely facing contact faces, and resilient means acting on said contact member and insulating body constantly biasing said contact member for movement in a predetermined direction.

16. An adapter for fuses and fuse receptacles comprising a member having a passage therethrough, a movable contact member comprising a cup-shaped member carried by said adapter member and located in a. portion of said passage, and resilient means acting between said contact member and adapter member constantly biasing said cup-shaped member for movement in a predetermined direction, said cup-shaped member having a thin bottom wall providing internal and external contact faces.

17. An adapter for fuses and fuse receptacles comprising a supporting member having a passage therethrough, a movable contact member carried by said supporting member comprising a cup-shaped member located in a portion of said passage and guided by said passage for movement lengthwise thereof, said cup-shaped member having a thin bottom wall providing both internal and external contact faces, and spring means acting on the peripheral portion of said cupshaped member and on said supporting member and operative to bias it for movement in a predetermined direction in said passage.

18. An adapter for fuses and fuse receptacles comprising a supporting member having a passage therethrough, a movable contact member carried by said supporting member comprising a cup-shaped member located in a portion of said passage and guided by said passage for movement lengthwise thereof, and having a thin bottom wall providing both internal and external contact faces and resilient means extended outwardly from the periphery of said cup-shaped member and bearing on said adapter and operative to constantly bias said cup-shaped member ior movement in a predetermined direction in said passage.

19. An adapter for fuses and fuse receptacles comp ising a supporting member having an interna recess and upper and lower passages leading in opposite directions from said recess to the ends of said member, a movable contact member in said recess comprising a cup-shaped member interposed between said passages and movable lengthwise of said lower passage, said cup-shaped member having a. thin bottom wall providing both internal and external contact faces and resilient means extended peripherally therefrom seated upon a face of said recess and operative to bias said cup-shaped member constantly for movement toward said recess.

JAIWES A. MCENTEE. 

